The present invention relates to a method and apparatus for coding of DC and AC coefficients for intra-macroblock digital video, in particular, when the current macroblock and/or a neighboring macroblock is interlaced (e.g., field) coded. Predictor coefficients from neighboring macroblocks are selected for use in differentially encoding the coefficients of a current macroblock to optimize coding efficiency. The coefficients are obtained from a spatial transformation such as the Discrete Cosine Transform (DCT), for example.
The invention is particularly suitable for use with various multimedia applications, and is compatible with the MPEG-4 Verification Model (VM) 8.0 standard (MPEG-4 VM 8.0) described in document ISO/IEC/JTC1/SC29/WG11 N1796, entitled "MPEG-4 Video Verification Model Version 8.0", Stockholm, July 1997, incorporated herein by reference. The MPEG-2 standard is a precursor to the MPEG-4 standard, and is described in document ISO/IEC 13818-2, entitled "Information Technology--Generic Coding of Moving Pictures and Associated Audio, Recommendation H.262, " Mar. 25, 1994, incorporated herein by reference.
MPEG-4 is a new coding standard which provides a flexible framework and an open set of coding tools for communication, access, and manipulation of digital audio-visual data. These tools support a wide range of features. The flexible framework of MPEG-4 supports various combinations of coding tools and their corresponding functionalities for applications required by the computer, telecommunication, and entertainment (i.e., TV and film) industries, such as database browsing, information retrieval, and interactive communications.
MPEG-4 provides standardized core technologies allowing efficient storage, transmission and manipulation of video data in multimedia environments. MPEG-4 achieves efficient compression, object scalability, spatial and temporal scalability, and error resilience.
The MPEG-4 video VM coder/decoder (codec) is a block- and object-based hybrid coder with motion compensation. Texture is encoded with an 8.times.8 Discrete Cosine Transformation (DCT) utilizing overlapped block-motion compensation. Object shapes are represented as alpha maps and encoded using a Content-based Arithmetic Encoding (CAE) algorithm or a modified DCT coder, both using temporal prediction. The coder can handle sprites as they are known from computer graphics. Other coding methods, such as wavelet and sprite coding, may also be used for special applications.
Motion compensated texture coding is a well known approach for video coding, and can be modeled as a three-stage process. The first stage is signal processing which includes motion estimation and compensation (ME/MC) and a two-dimensional (2-D) spatial transformation. The objective of ME/MC and the spatial transformation is to take advantage of temporal and spatial correlations in a video sequence to optimize the rate-distortion performance of quantization and entropy coding under a complexity constraint. The most common technique for ME/MC has been block matching, and the most common spatial transformation has been the DCT.
Additionally, in certain situations, coding efficiency may be improved when macroblocks are INTRA coded, e.g., without reference to a temporally subsequent or previous predictor macroblock. INTRA coding may be desirable for an image sequence with rapid motion, a scene change, or rapid changes in lighting conditions, where there may be little frame-to-frame correlation. Coding efficiency may further be improved by differentially encoding the DCT coefficients of a current block using the coefficients of a neighboring block as predictor coefficients.
However, with coding schemes such as MPEG-4, it is possible to have both frame mode and field mode macroblocks next to one another in a video object plane (VOP) or other image area. Additionally, field mode macroblock may be reordered or non-reordered in an adaptive coding scheme. Accordingly, it would be desirable to have a system for selecting predictor coefficients for differentially coding the AC and DC DCT coefficients of a current INTRA coded block, where the current block and/or the neighboring blocks are coded in a frame mode, non-reordered field mode, and/or reordered field mode.
The system should further provide non-linear quantization of DC transform coefficients.
The present invention provides a system having the above and other advantages.